Noise and reverberation sonar range computer

ABSTRACT

This disclosure is directed to a slide rule type device for determining the noise and reverberation which limits sonar performance. The device includes a base and cursor upon which related information has been placed. The cursor is operatively related with the data on the base such that associated information may be used for determining noise and reverberation for sonar equipment.

'United States Patent T1 1 Barron 1 1 Dec. 2, 1975 15 1 NOISE ANDREVERBERATION SONAR 2.967.662 6/1961 Bauer 235/61.5 s RANGE COMPUTER3.266.721 8/1966 Barron 235/61 [76] Inventor: Daniel Barron, 9326Edmonston primary Fcinberg Road Greenbelt 20770 Attorney, Agent. orFirmR. S. Sciascia; Arthur L. 22 Filed; June 1 1971 Branning; Melvin L.Crane This disclosure is directed to a slide rule type device [52] (1.8.CI. 235/61 B; 235/89 R for determining the noise and reverberation which[51] Int. Cl. G06C 3/00 limits sonar performance. The device includes abase [58] Field of Search 235/61 R, 61.5 R, 61.5 DF. and cursor uponwhich related information has been 235/61.5 T, 61.5 B. 69. 70, 61 B, 89R placed. The cursor is operatively related with the data on the basesuch that associated information may be [561 References Cited used fordetermining noise and reverberation for sonar UNITED STATES PATENTS q p2,569.454 10/1951 Cole 235/70 R 4 Claims, 3 Drawing Figures mm 2 O.

- INVENTOR DANIEL BARRON ATTORNEY 0 8w m h US. Patent Dec. 2, 1975 F/GZSheet 2 of ARGET BELOW THERMOCLINE 0 THERMAL DEPTH IN FEET d v lllllllllIIO I l lillllllllll I00 liO I I I0 R2 llllllill US. Patent Dec. 2, 1975Sheet 0f3 3,924,104

NOISE AND REVERBERATION SONAR RANGE COMPUTER STATEMENT OF GOVERNMENTINTEREST The invention described herein may be manufactured and used byor for the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION This invention relates to a hand operatedcomputation device and more particularly to a computation device fordetermining and correcting for noise and reverberation which limitssonar operation.

SUMMARY OF THE INVENTION This invention is directed to a hand operatedcomputer device having a base upon which noise and reverberation datahas been placed in combination with range in Kiloyards, thermal depth infeet, and frequency data have been placed. The cursor includes thereonnoise and reverberation curves in combination with spaced parallel lineswhich are asymtotes to the curves. The cursor also includes spaced linesfrom which ranges may be obtained for desired probabilities ofdetection.

STATEMENT OF THE OBJECTS It is therefore an object of the presentinvention to provide a hand operated computation device for computingambient noise and reverberation which limits sonar performance.

Another object is to provide a simple efficient, inexpensive computationdevice for computing noise and reverberation which limits sonarperformance.

Still another object is to provide a noise and reverberation computationdevice which may be used by unskilled as well as skilled personnel.

Other objects and advantages of the invention will become obvious toothers upon reading the following description of the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a top view of thedevice; FIG. 2 illustrates the base with data thereon; and FIG. 3illustrates a separate view of the cursor.

DESCRIPTION OF THE DRAWINGS Now referring to the drawings there is shownby illustration a computation device for correcting the performance of asonar in determining range. As shown, the device includes a base 10,upon which data has been placed. Above the base there is located aslidable cursor 11 which includes reference lines as well as frequencycorrection information.

The base may be formed of a solid material such as plastic, metal, woodor any other desired material and of rectangular shape. Across thelength of the bottom, there are placed four linear scales 13-16 ofnumerical information graduated in accordance with data obtained by wellknown equations for well known sonar equipment. Two of the linear scalesl3 and 15 are for noise and scales l4 and 16 are for reverberation. Theletters of R1, N1, R2, and N2 refer to noise and reverberation, aslimiting factors, and the numbers by the letters refer to atwo-dimensional or a one-dimensional 2 transducer. The figures on thescales are formed by the following equations:

R1 Reverberation for a one-dimensional transducer I l Vf! cos 0 2 IcosO[200 2350 1 N1 Noise for one-dimensional transducer R2 Reverberation fortwo-dimensional transducer Af t Vfl C05 6 2 R2 [cos 0 [200 T 2350 1 N2Noise for two-dimensional transducer PA! PA: N2 10 log W: 2V+l0 log Wwhere P Acoustic power A Transducer Area (cm) t= pulse length(milliseconds) n sea state, characterizing ambient noise l= transducerlength (cm) 0 aspect angle from 0 to 90 Cos 0 Cos 0 from 0 to 0.173 from80 to f frequency fnl, fn2 Optimum frequency for noise limited range Vtarget speed (Knots) V speed of carrier (knots for airborne equipment)If the directivity is D at a frequency f, then the area A may be takenfrom 10 log A 32.7 D 20 logf.

If the directivity is D at a frequency f, then the length may be from 10log l= 18.8 D l0 logf.

Immediately above the scales on the base, there is a logarithmiccoordinate system tilted at a 45 angle with respect to the linear scaleson the bottom portion of the base. The lines 17 of the logarithmic scalethat extend upwardly and to the right indicate the thermal depth, d,values in feet (20-400) which are shown along the bottom near the edgeof the scales. The lines 18 extending upwardly to the left indicaterange in Kiloyards, the values are shown along the upper left and rightedges of the coordinate system.

Further, there is shown a plurality of parallel lines 21 extending fromthe thennal depth scale upwardly to a curved line 22. The curved line isused to determine the range of a target below the thermocline. The curveis such that the parallel lines extend from the edge of the curved lineends at the corresponding range. The curved line is determined by wellknown sonar formula which relates depth to range.

The two straight lines Fnl and Fn2 serve to determine the optimumfrequency for a noise limited range. The lines are determined forspecific equipment and the lines relate depth to frequency:

The noise and reverberation scalaf liifoi'matioii is related to thethermal depth in feet 55B Htitfii: Iii Kiloyards by use of a cursorwhich is rfiBVEibiE filBhg the base. The cursor contains thereon threecurves 2 6, 27, and 28 which extend from the upper left corner towardthe bottom and right side. The curves are formed from data relating thenoise and reverberation to the thermal depth in feet and the range inKiloyards. The cursor includes a vertical line 31 that extends acrossall ofthe scalar lines. This line is used in determining the nominalrange, that is, the range obtained with a 50% probability of detection.The short vertical lines 32-35 (10,-

30, 70 and 90) on each side ofthe long line for each of the scalar linesserve to find the ranges obtained with the respective probabilities. Theslope of the lines on the cursor are such that when the probability lineselected is placed over the corresponding noise or reverberation scale,the point of interception of the thermal depth line with thecorresponding curve will give the range. The range of operation will bewith the smaller range, as determined for the noise and reverberation,corresponding to the conditions. The noise and reverberation may bedetermined by, the above formulas depending on the equipment and thedifferent parameters that affect the sonar signal.

Operation of the computation device for determining sonar range withequipment operating with the following parameters;

P 32W t 120 milisec f= 20Kc N 4 A 420cm Thermal depth 150 feet targetspeed 3 Knots; 6 60 (target above the thermocline) is as follows:

Step 1:

Calculate characteristic figures N2 and R2 from the formulas previouslygiven above for the 'above given conditions:

These values may also be obtained by use of a chart which shows a directrelationship between ships speed, I target speed and'the Figure ofmerit.

26 (N2). Read the value of Range r of this point which is found to be4.2 Ky. This is the hois'e limited range r.

. Step 4:

Move the cursor so that the 50 line is over 29.2 of the R2 scale, followline d 150 to its intersection with curve 28 RlR2). Read the Range valuer of this point which is 3.9 kyd. This is the reverberation limitedrange, r,; at optimum frequency. I

Step 5:

Estimate the correction to corresponding to the operational frequency.No such correction is required for reverberation limited rangefound bythe computer.

Step 6: Find the optimum frequency'fo by following the line r= r,, (4.2ky) to its intersection with the line fn2 going" right and up from thispoint, read f0 on the upper edge at 17 Khertz.

Step 7:

The range corresponding to an operating frequency fl, r, is smaller thanthe range at optimum frequency, r by a fraction b which is for a roughestimate;

Iffdeviates from 0 by less than 20% the range correction is smaller than2%. v

For more precise information, form the ratio f/fo and read with thisvalue as abscissa, the ordinate from curve R2(db) subtract this from N2and read r for the reduced characteristic figure. This is the noiselimited range rffor a frequencyf. In the example f0=20,f=17 for thisabscissa C2 has the f/fo 1.18 value of 0.6 db. The reducedcharacteristic figures is 73.4 0.6 72.8;

'the noise limited range is 4.15 ky instead of 4.2 kyd.

EXAMPLE 2 With data as in example 1, but target below the thermocline,proceed as follows:

Step I:

Set cursor at N2 73.4.

Step 2:

From the point on d scale, follow a line to the left and up to itsintersection with the curve 22 marked target below thermocline. Fromthis point follow the line d constant (62 in the example) up to theintersection with curve N2 giving r-=3.3 Kyds.

Step 3:

apply the correction for non-optimum frequency to r Similarly, with thecursor set at R2 29.2 follow the line d 62 to intersection with curveRlR2 giving r =2.4 Kyd. Note: In any given position of the cursor theranges can be read for all depths for thermocline represented on thecomputer for target above" as well as for target below" the thermocline.

EXAMPLE 3;

Data as in Example 1, ranges to be determined for a probability otherthan 50%. To find the noise limited range for a probability of say 10%slide cursor to a position where the index line 10" belonging to scaleN2 is set at 73.4 on scale N2 proceeding as before, one finds r 5.0 kyfor d= 150 ft. To find the reverberation limited range for a probabilityof 10%, slide cursor to a position where the indices 10, belonging toscale R2 is set at 29.2 on scale R2 proceeding as in paragraph 5 above,one finds r,; 6.4 Kyd for d= 150 ft. The probability at other values maybe obtained by moving the cursor such that the desired value is over thedetermined value on the noise and reverberation scales as set forthabove.

The curve 30 on the left of the device may be used for determining acorrection factor which may be used to find'the final operable range asset forth above.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:

1. A device for determining noise and reverberation that limits sonarperformance, which includes,

a base,

a plurality of rows of different scale values extending in parallelacross the bottom of said base,

said base including thereon a portion of a logarithmic scale extendingacross said base at 45 angle above said scale values,

said logarithmic scale lines extending to the right and upwardlyrepresenting depth in feet,

said depth values indicated along the bottom of said logarithmic scale,

said logarithmic scale lines extending upwardly and to the leftrepresenting range values in kiloyards,

said range values aligned along the sides of said logarithmic scale,

a cursor positioned over said base for linear movement relative to saidbase,

said cursor including thereon three curved lines and a plurality ofvertical parallel lines,

said vertical lines relating said curved lines to depth and range inaccordance with probability of detection,

said vertical lines aligning with different rows of said plurality ofrows of different scale values on said base, and

a single probability line on said cursor that extends across the totalnumber of rows of said plurality of rows of different scale values onsaid base.

'2. A device as claimed in claim 1; wherein,

said base includes two parallel lines extending across said logarithmicscale from the bottom edge to the top edge,

optimum frequency values extending across the top of said logarithmicscale, and

said pair parallel lines are related to said optimum frequency valuesnoted on the base.

3. A device as claimed in claim 2; which includes,

a curve extending across said logarithmic scale for determining rangeand reverberation ofa sonar for a target below the thermocline.

4. A device as claimed in claim 3; which includes,

a correction scale in combination with said logarithmic scale forcorrecting the optimum frequency to an operating frequency.

1. A device for determining noise and reverberation that limits sonarperformance, which includes, a base, a plurality of rows of differentscale values extending in parallel across the bottom of said base, saidbase including thereon a portion of a logarithmic scale extending acrosssaid base at 45* angle above said scale values, said logarithmic scalelines extending to the right and upwardly representing depth in feet,said depth values indicated along the bottom of said logarithmic scale,said logarithmic scale lines extending upwardly and to the leftrepresenting range values in kiloyards, said range values aligned alongthe sides of said logarithmic scale, a cursor positioned over said basefor linear movement relative to said base, said cursor including thereonthree curved lines and a plurality of vertical parallel lines, saidvertical lines relating said curved lines to depth and range inaccordance with probability of detection, said vertical lines aligningwith different rows of said plurality of rows of different scale valueson said base, and a single probability line on said cursor that extendsacross the total number of rows of said plurality of rows of differentscale values on said base.
 2. A device as claimed in claim 1; wherein,said base includes two parallel lines extending across said logarithmicscale from the bottom edge to the top edge, optimum frequency valuesextending across the top of said logarithmic scale, and said pairparallel lines are related to said optimum frequency values noted on thebase.
 3. A device as claimed in claim 2; which includes, a curveextending across said logarithmic scale for determining range andreverberation of a sonar for a target below the thermocline.
 4. A deviceas claimed in claim 3; which includes, a correction scale in combinationwith said logarithmic scale for correcting the optimum frequency to anoperating frequency.